In recent years, spin-electronic devices utilizing a spin-polarized electron have been studied worldwide. In, e.g., a hard disk drive, the magnetization direction of the medium is reversed by a magnetic field generated from the magnetic head to execute a write-in. In a magnetic random access memory, an electric current magnetic field totally generated by supplying currents to two write-in lines is applied to a cell to control its magnetization direction. These magnetization direction control methods utilizing an external magnetic field have a long history and are regarded as established techniques.
On the other hand, along with the recent progress in nanotechnology, bit or cell size of magneto-resistance devices has been reduced. Accordingly, magnetization control must locally be done on a nanoscale.
However, localization of the magnetic field is difficult, because a magnetic field fundamentally spreads spatially. This causes the problem of “cross talk”. That is, even when a specific bit or cell is selected to control its magnetization direction, the magnetic field spreads to adjacent bits or cells and executes an incorrect write-in on them. If the magnetic field generation source is made small to localize the magnetic field, no sufficient magnetic field can be generated.
Then, a “current direct driving magnetization reversal method” to avoid the problem has come to attract attention (e.g., F. J. Albert, et al., Appl. Phy. Lett. 77, 3809 (2000)). In this method, an electric current is supplied to a magnetic layer of a magneto-resistive effect element to spin-polarize electrons. The spin-polarized electrons are caused to pass through the target magnetic layer to reverse its magnetization. More specifically, when the angular momentum of the spin-polarized electrons is transmitted to and acts on the angular momentum of the magnetic materials whose magnetization is to be reversed, the magnetization direction of the magnetic material is reversed.
When this method is employed, the current can be caused to more directly act on a magnetic material on a nanoscale, as compared with the above-described current magnetic field write-in methods. The current necessary for magnetization reversal can be caused to also reduce fundamentally according to the miniaturization of the magneto-resistive effect element. Hence, this technique of “spin injection magnetization reversal” contributes to realizing spin electronics devices such as high-density hard disks or MRAMs.
The magnetic recording element was proposed in JP-A 2004-193595 (Kokai). The magnetic recording element is formed with a multilayer to reduce the current density for “direct-current-driving magnetization reversal.” The multilayer is formed with two magnetically fixed layers whose magnetization directions are anti-parallel, and includes a magnetic recording layer whose magnetization direction is variable. Further, the multilayer includes intermediate layers provided between the magnetic recording layer and the magnetically fixed layers.